Dyad S400 is a state-of-the-art true fully balanced hybrid power amplifier in which voltage amplification is done by all vacuum tubes. S400 employs the patented Dual Balanced Feedback Topology (DBFT) and proprietary high current buffer amplifier (HCBA). The design of S400 is highlighted in the following diagram.
Since there are two out-of-phase signals in a fully balanced amplifier, two HCBAs are used for the output stage. Each HCBA has the following properties:
* Unity voltage gain
* High speed and high current gain
* High power capacity
* Input and output are maintained at DC ground level automatically
* Protect output for over current, output DC offset and overheat
* Stable with and without global feedback applying to it
One HCBA amplifies signal of one phase and the other HCBA amplifies signal of the opposite phase. Since the input stage and second stage use all vacuum tubes for signal amplification, and the HCBAs have unity voltage gain, the overall sound has retained very much to what we expect from a tube power amplifier. But it has advantage over vacuum tube power amplifier in terms of high current drive provided by the semiconductor buffer amplifier at the output. The fully balanced hybrid power amplifier eliminates a frequency dependent and bulky output transformer altogether. Finally, a fully balanced amplifier has an additional advantage of having a strong immunity against common mode noises.
|Dual Balanced Feedback Topology (DBFT) and high current buffer amplifier (HCBA).|
- Fully balanced input (also has separate RCA input).
- Fully balanced output (no loudspeaker terminal is connected to a ground terminal).
- Patented Dual Balanced Feedback Topology (DBFT) improves signal linearity and audio fidelity.
- Signal amplification is handled by all vacuum tubes.
- Output current amplification is handled by all solid-state MOSFET high current buffer amplifier (HCBA) output stage.
- HCBA output stage is protected for over current, DC offset and over heat.
- The S400 continuously monitors the vacuum tubes and the solid-state transistors packed HCBA. If a vacuum tube is operated outside of its allowable operation region, or any HCBA is detected with over current, high DC offset voltage or over heat, a LED lamp will turn to red. And the S400 will shut down automatically.
- Audio grade low noise toroid power transformer is used.
- Audio grade signal capacitors are used for signal coupling.
- Soft-start circuit reduces the inrush current when switching on. It also ensures that in the first 45 seconds the vacuum tubes can warm up properly. This prolongs life of all rectifying diodes, power supply filtering capacitors and vacuum tubes.
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